Hi, is the HK MTR Tourist Pass only available for a single day use at HK$55?

Yes, Tourist Day Pass is valid for one day on MTR and Light Rail (except Airport Express, MTR Bus, East Rail Line First Class and travel to/from Lo Wu or Lok Ma Chau stations). It costs HKD 65, not HKD 55. It cannot be topped up.

If you plan to stay in HK for about one week, you are advised to buy Standard Octopus Card. The card is applicable on MTR, Light Rail, buses, ferries, taxis, trams, etc. You need to pay HKD 50 as the refundable deposit, and HKD 50 as the stored value. Have a try! :)